Neodymium magnet is a sintered product comprising neodymium (Nd), iron oxide (Fe), and Boron (B) as main components, which is featured by very excellent magnetic property. Although demand for this high property neodymium bulk magnet has increased, imbalance of demand and supply of the rare-earth elements obstructs supply of high performance motor necessary for next generation industry.
Samarium cobalt magnet which comprises samarium and cobalt as main component is known to have very excellent magnetic property next to the neodymium magnet, but the problem of demand and supply of samarium, one of rare-earth elements, also causes rise of production cost.
Ferrite magnet is a low priced magnet with stable magnetic property which is used when strong magnetic force is not required. Ferrite magnet is produced by powder metallurgy in general, and usually black colored. The chemical form of ferrite magnet is XO+Fe2O3, wherein X may be barium or strontium depending on its uses. The ferrite magnet is classified into the dry-processed or wet-processed according to its manufacturing methods, or into the isotropic or anisotropic according to its magnetic direction. The ferrite magnet is a compound consisting of oxides, therefore it is an insulator and has almost no loss of high frequency such as excessive current loss, even if it is operated in a magnetic field of high frequency. The isotropic magnet has lower magnetic force than anisotropic, but has several advantages such as low price and free attachment. The ferrite magnet has been used in diverse applications such as D.C motor, compass, telephone, tachometer, speaker, speed meter, TV, reed switch, and clock movement, and has several advantages such as its light weight and low price. However, the ferrite magnet has also a disadvantage that it does not show an excellent magnetic property enough to substitute high priced neodymium bulk magnet.
Meanwhile, a core-shell structured nanoparticle means a material having a structure where a shell substance surrounds a core substance located in the center. As the core-shell structured nanoparticle provides multifunctional nano-materials having at least two (2) properties depending on the properties of the substances contained in each layer, there have been a number of researches and developments on the core-shell structured nanoparticles by providing different combinations of metal-metal, metal-ceramic, metal-organic, and organic-organic structure. It has been known that the core-shell structured nanoparticles has a high applicability to various areas due to its combined functionalities of magnetic, fluorescent, acid-resistant, and anti-abrasion property.
Until now, there has been a limitation to the substances contained in a core or shell structure, and most of the researches have been done on these limited substances only. Under this situation, it is considered that there are great future possibilities in re-searching and developing a new core-shell structured nanoparticle by exploring new substances besides the one conventionally researched so far, and combining these materials, thereby providing new properties.
Methods to obtain core-shell structured nano-particle powder include co-precipitation, spraying, electrolysis and sol-gel method, and reverse micelle method.
For instance, U.S. Pat. No. 7,547,400 uses a reverse micelle method to prepare a nano-sized nickel-zinc ferrite and Korea Patent Application No. 10-2010-0029428 uses a sol-gel method to prepare nano-iron powder.
Among these, Korea Patent Application No. 10-2010-0029428 embodies a core-shell dual structure, but this invention shows limited physical and magnetic properties like conventional soft magnetic material, since both of the core and shell consist of soft magnetic substances only.
Throughout the present application, several patents and publications are referenced and citations are provided. The disclosure of these patents and publications is incorporated into the present application in order to more fully describe this invention and the state of the art to which this invention pertains.